Image forming apparatuses such as printers, facsimiles, copiers, plotters, and multifunction apparatuses that print, fax, copy, and so on, also include an ink jet recording apparatus, which includes a liquid droplet discharge head to discharge ink liquid droplets to perform image forming on a recording medium.
In the ink jet recording apparatus disclosed in JP 2006-301335A, as shown in FIG. 1, an image is formed by discharging an ink on a sheet of paper 203 that is the recording medium while a carriage 202 is moved to scan the recording medium in a main scanning direction (a direction shown by the double-headed arrow “b” in FIG. 1). The carriage 202 is slidably supported in the main scanning direction by two guide rods, a main guide rod 205 and a secondary guide rod 206, extending between the left and right side plates 204A and 204B. The carriage 202 is moved to scan in the main scanning direction by a primary scanning motor, not shown, through a timing belt, not shown, perpendicular to a sub-scanning direction in which the recording medium 203 is conveyed (a direction indicated by the arrow “a” in FIG. 1).
The carriage 202 includes recording heads 201, which discharge liquid droplets of black ink (K), cyan ink (C), magenta ink (M), and yellow ink (Y), a circuit board, not shown, to provide a drive signal to the recording head 201, and a recording head unit incorporating the recording heads 201 and sub tank 207 to store the ink to be supplied to the recording heads 201. Each color ink is supplied to the sub-tank 207 of the recording head 201 from the ink cartridge 209 for each color through the supply tube 208 for each color. In order to send the recording medium 203 fed from a recording medium feed unit, not shown, to the lower side of the recording head 201, an electrostatic conveyance means which, in the present invention, is a conveyance belt 210 adsorbs the recording medium 203 electrostatically and conveys it to a position facing the nozzle surface of the recording head 201.
The conveyance belt 210 is an endless belt entrained around the conveyance roller 211 and the tension roller 212 that circulates in the sub-scanning direction shown by arrow “a” in FIG. 1. The conveyance belt 210, the conveyance roller 211 and the tension roller 212 and a holding member that holds the conveyance roller 211 and the tension roller 212 around which the conveyance belt 210 is entrained together form a conveyance belt unit. Further, a charging roller, not shown, that charges the surface of the conveyance belt 210 is provided. The charging roller is disposed to contact the front layer of the conveyance belt 210 and is driven to rotate to follow the rotation of the conveyance belt 210. As shown in FIG. 2A, positioning in the main scanning direction and the sub-scanning direction is carried out by fitting the roller shaft of the conveyance roller 211 to the bearing member 213. The roller shaft of the tension roller 212 is engaged with the bearing member 214 in a direction perpendicular to the axis. The conveyance belt is circulated to move in the belt conveyance direction by rotating the conveyance roller 211 to rotate with a sub scanning motor, not shown, through the timing belt. In order to maintain the landing position of ink discharged from the recording head onto the recording medium, or avoid damage due to contact of the recording head with the recording medium, the electrostatic adsorption conveyance means conveys the recording medium while keeping a predetermined short distance between the recording head and the recording medium.
The surface of the conveyance belt gets dirty and is damaged by scattering ink, paper particles, dust generated while printing and wear and tear of the conveyance belt. Then, the adsorption performance of the recording medium is degraded, necessitating replacement of the conveyance belt.
Replacement of the conveyance belt is as follows: In the ink jet recording apparatus disclosed in JP-2011-031606-A, as shown in FIG. 2A, the primary guide rod 205 and the secondary guide rod 206 are provided in a space above the conveyance belt 210 of the conveyance belt unit. On the primary guide rod 205, the carriage 202 is slidably mounted via a mounting member 215. When the belt conveyance unit is mounted and removed, the mounting member 215 is removed at the beginning. On the other hand, since only a part of the carriage 202 is suspended to the secondary guide rod 206, the carriage 202 can be removed upward from each guide rod. When the conveyance belt unit is removed after removing the carriage 202, as shown in FIG. 2B, there is almost no space between the primary guide rod 205 and secondary guide rod 206 disposed above the conveyance belt 210 and the conveyance belt 210. Accordingly, the two guide rods disturb the movement of the conveyance roller 211 so that the conveyance roller 211 cannot be removed from the bearing unit 213. As a result, it is difficult to remove the conveyance belt unit from the main body of the apparatus only by removing the carriage 202.
It is conceivable that the two guide rods can be removed from the main body of the apparatus, however, it is necessary to remove the fixed member provided at both side surfaces and other units of apparatus to remove the two guide rods, which is complicated and time-consuming.
In addition, the image forming apparatus disclosed in JP 2006-301335A described above includes a spur holder including a spur roller supported by an elastic body, such as a spring, to oppose to a recording medium output roller. Since the spur roller contacts the surface of the recording medium with a point contact, the contact area with the recording medium surface (image surface) is minimized, and accordingly, the trace of the spur rollers is reduced to be the minimum while maintaining the power to convey the recording medium, thereby, preventing image forming failure from occurring.
However, in the image forming apparatus disclosed in JP 2006-301335A, the spur holder is moved between a retracted position and an engaged position for each piece of recording medium, accordingly, there is a possibility that the spur holder may not be moved to the retracted position or the engaged position correctly due to the aging of a solenoid or a spring, etc. of the spring moving system. When the spur holder is moved excessively to the engaged position, the spur roller contacts the recording medium deeply to press the recording medium excessively so that traces of the spur roller remain.
Further, since the spur holder is mounted in the moving means by fastening means such as a screw, etc., the spur holder should be removed from the moving means when the spur holder is exchanged. Accordingly, it is not easy to exchange the spur holder.
The present invention is conceived in the view of the problems described above, therefore, and provides an image forming apparatus in which the replacement of the spur holder is easy and moreover prevents the image forming failure due to the trace of the spur roller on the recording medium from occurring.